Tundish impact pad

ABSTRACT

A tundish impact pad comprises the body of refractory material capable of withstanding contact with molten steel. The body comprises a base having an impact surface for molten steel, and an outer side wall extending upwardly from the impact surface. The outer side wall extends around the base to completely enclose it, an annular body portion connected to the side wall and providing a top surface substantially parallel to the impact surface and defining an opening into which molten steel can be poured. The lower surface of the annular body portion and the inner face of the side wall define a recess having an undercut portion extending continuously around and above the impact surface. A first portion of the top surface is at a lower level than the remainder at the top surface and the recess beneath the first portion of the top surface has a smaller cross-section than the remainder of the recess. The impact pad is particularly useful with a longitudinally-extending tundish having a steel inlet zone toward the end opposite to the outlet zone(s).

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase of PCT/GB97/00899 with theinternational filing date of Apr. 1, 1997.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a tundish impact pad, i.e. a pad of erosionresistant material positioned on the floor of a tundish to receive theincoming stream of molten metal poured into the tundish from a ladle.

There have been various recent proposals to improve the design of impactpads, particularly with a view to eliminating, or at least reducing,surface turbulence in a continuous casting tundish, to minimise slagentrainment within the liquid steel bath in the tundish, to preventbreak-up of tundish flux cover and reoxidation of the liquid steel bathand to ensure a proper flow path. These designs, essentially, haveincluded a base for the pad and upstanding walls around the perimeter ofthe base to define an opening into which the molten metal stream isreceived.

Thus, for example, in U.S. Pat. No. 5,169,591 is disclosed an impact padhaving a base to receive an incoming ladle stream and one or moresidewalls extending upwardly along the periphery of the base. Eachsidewall has an inner surface having an undercut portion facing theincoming ladle stream and extending along the length of the innersurface, thereby providing a shaped surface to receive and reverse thedirection of fluid flow generated by the incoming ladle stream.

U.S. Pat. No. 5,358,551 discloses an impact pad having a bottom impactsurface and an endless sidewall extending upwardly from the bottomimpact surface and defining an opening into which molten metal ispoured. The inner surface of the endless sidewall includes an annularportion which extends inwardly and upwardly towards the opening.Preferably the inner surface of the sidewall curves continuously fromthe bottom impact surface to a vertical wall defining the opening.

It is an object of the present invention to provide an improved impactpad.

It is a further object to provide an impact pad which results inimproved flow characteristics of molten steel poured into a tundish,particularly for a longitudinally-extending tundish in which the steelinput zone and steel outlet zone(s) are towards opposite ends of thetundish.

Accordingly, in one aspect the invention provides a tundish impact padcomprising a body of refractory material capable of withstanding contactwith molten steel, the body comprising a base having an impact surfacefor molten steel, an outer sidewall extending upwardly from the impactsurface, the outer sidewall extending around the base to completelyenclose it, an annular body portion connected to the sidewall andproviding a top surface substantially parallel to the impact surface anddefining an opening into which molten steel can be poured, the lowerface of the annular body portion and the inner face of the sidewalldefining a recess having an undercut portion extending continuouslyaround and above the impact surface, characterised in that a portion ofthe top surface is at a lower level than the remainder of the topsurface and the recess beneath the portion of the top surface is ofsmaller cross-section than the remainder of the recess.

Preferably the lower face of the annular body portion and the inner faceof the sidewall provide a continuous curved surface which, at its lowerend, merges into the impact surface of the base thereby providing aconcave recess around the base, the recess having two discontinuities orsteps, i.e. one at each end of the smaller recess portion.

The impact pad is preferably four-sided in plan view and, in aparticularly preferred embodiment, it has one pair of parallel sides,(defined by the outer surface of the sidewall) i.e. it is wedge-shaped.In this latter embodiment, the longer parallel side preferably includesthe first portion of the top surface, i.e. includes the lower topsurface portion, and the smaller recess. Alternatively, the pad may be,for example, rectangular in plan view.

The smaller recess is preferably not coterminous with the lower topsurface portion and it is especially preferred that the smaller recessportion does not extend as far as the ends of the lower top surfaceportion, i.e. the smaller recess portion is not as long as the lower topsurface. Thus, in the preferred wedge-shaped pad construction, the lowertop surface portion stops a little short of each end of that sidewall toprovide a step up to a top surface level with the remainder of thesurface extending around the other sides of the pad and the smallerrecess portion extends underneath the lower top surface portionsufficiently that each of its ends overlaps the recess in its respectiveadjacent side of the pad but stops short of the aforesaid step.

In this embodiment, therefore, there is in effect a cut-out portion inthe top surface along one of the four sides of the pad.

As indicated above, the impact pad of the invention is particularlyintended for use with a longitudinally-extending tundish having a steelinlet zone towards the end opposite to the outlet zone(s).

Accordingly, in another aspect the invention provides a tundish havingan inlet zone adjacent a first end thereof and an outlet zone adjacentthe opposite end thereof, an impact pad positioned on the floor of thetundish in the inlet zone, the impact pad comprising a body ofrefractory material capable of withstanding contact with molten steel,the body comprising a base having an impact surface for molten steel, anouter sidewall extending upwardly from the impact surface, the outersidewall extending around the base to completely enclose it, an annularbody portion connected to the sidewall and providing a top surfacesubstantially parallel to the impact surface and defining an openinginto which molten steel can be poured, the lower face of the annularbody portion and the inner face of the sidewall defining a recess havingan undercut portion extending continuously around and above the impactsurface, characterised in that a portion of the top surface is at alower level than the remainder of the top surface and the recess beneaththe portion of the top surface is of smaller cross-section than theremainder of the recess and the pad is positioned with the first portionof the top surface facing to the first end of the tundish.

In the particularly preferred embodiment, therefore, where the impactpad is of wedge-shape, the longer parallel side of the pad is positionedfacing the first end of the tundish.

The impact pads of the invention have been found to be particularlyuseful in reducing surface turbulence in tundishes of the type describedabove and are equally useful in tundishes which are generallyrectangular in plan view and tundishes which are generally of wedgeshape, i.e. with two parallel sides, in plan view. Moreover, the flowpatterns of the molten metal within the tundish can be improved overthose resulting from use of conventional impact pads.

The impact pads may be formed from a castable refractory compositioncapable of withstanding continuous contact with molten metal, inparticular molten steel such as is used in continuous castingoperations. Usually a standard medium-to-high alumina refractory with analumina content in the range of about 55% to 85% by weight is desirable.Where a basic refractory is preferred because of steel chemistry, it ispreferred that a magnesia-based refractory composition be utilised, withMgO in the range of about 58% to 93% by weight.

The invention is now described by way of example only with reference tothe accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an impact pad of the invention;

FIG. 2 is a section on line II--II of FIG. 1;

FIG. 3 is a view in the direction of arrow A of FIG. 1;

FIG. 4 is a diagrammatic end profile of the pad in the direction ofarrow A in FIG. 3;

FIG. 5 is a plan view of one form of tundish of the invention;

FIG. 6 is a plan view of another form of tundish of the invention; and

FIG. 7 is a section on line VII--VII of FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIGS. 1 to 4, a tundish impact pad 10 is of wedge-shaped plan formhaving two parallel sides 11 and 12, of which side 11 is longer, and twonon-parallel sides 13 and 14 of equal length.

The pad has a base 15 and an impact surface 16 to receive a stream ofmolten steel. An outer sidewall 17 extends upwardly from the impactsurface 16 and extends completely around the base, i.e. it provides allfour sides 11, 12, 13 and 14 of the pad. An annular body portion 18 isconnected to the side wall and provides a top surface 19 substantiallyparallel to impact surface 16 and defines an opening 20 into whichmolten steel can be poured.

The lower face of the annular body portion 18 and the inner face of thesidewall 17 define a recess 21 having an undercut portion 22 whichextends around and above impact surface 16.

The longer side 11 of the pad has a sidewall 17A connected to an annularbody portion 18A having top surface 19A at a lower level than theremainder of the top surface 19. The lower face of annular body portion18A and the inner face of sidewall 17A define a recess 21A having anundercut portion 22A. Recess 21A is of smaller cross-section than recess21.

As shown most clearly in FIGS. 1 and 4, the lower top surface 19A doesnot extend for the full length of side 11 of the pad. It stops a littleshort of each end of that side to provide a step 23 up to a corner topsurface portion 19C which is level with surface 19 extending around theother sides of the pad.

As shown most clearly in FIGS. 1 and 3, recess 21A extends beneath topsurface 19A but stops short of step 19C at each end of top surface 19A.It does, however, extend sufficiently to overlap with recess 21 in thesidewalls 17 of sides 13 and 14 of the pad.

FIG. 5 shows the impact pad 10 of FIGS. 1 to 4 in position on the floor31 of a tundish 30. The tundish is longitudinally-extending and wedgeshape in plan and has an inlet region 32 adjacent its narrow end 30A andtwo outlets 33 towards its wider end 30B. Impact pad 10 is positioned inthe inlet region 32 with its longer side 11 facing narrow end 30A of thetundish.

FIGS. 6 and 7 show a similar arrangement for a tundish 34 of rectangularplan. This tundish has an inlet region 35 and an outlet 36 towards itsopposite ends 34A and 34B respectively. Impact pad 10 is againpositioned on floor 37 in the inlet region with its longer side 11facing end wall 34A of the tundish.

The tundish in FIG. 7 is shown to have a pouring tube 35A to directincoming steel into the impact pad 10 and a dam 38, which may beprovided where necessary and as is conventionally known.

Steel flowing into impact pad 10 flows outwardly towards the sidewallsafter hitting impact surface 16 and is then turned in recesses 21 and21A to flow out of the pad over surfaces 19 and 19A. As indicated by thearrows in FIGS. 5 and 6, flow towards walls 30A and 34A respectively isover lower top surface 19A.

This arrangement has been found to reduced markedly the surfaceturbulence created in the tundish and the improved flow paths createdresult in cleaner steel production.

What is claimed is:
 1. A tundish impact pad comprising:a body ofrefractory material capable of withstanding contact with molten steel,said body comprising a base having an impact surface for molten steel,an outer sidewall extending upwardly from the impact surface, said outersidewall extending around said base to completely enclose said base, anannular body portion connected to said sidewall and providing a topsurface substantially parallel to said impact surface and defining anopening into which molten steel can be poured; said lower surface ofsaid annular body portion and said inner face of said sidewall defininga recess having an undercut portion extending continuously around andabove said impact surface; and wherein said top surface is at a lowerlevel than the remainder of said top surface and said recess beneathsaid portion of said top surface is of smaller cross-section than theremainder of said recess.
 2. A tundish impact pad according to claim 1wherein said lower face of the annular body portion and said inner faceof said sidewall provide a continuous curved surface which at its lowerend merges into said impact surface of said base thereby providingaround said base a concave recess having two discontinuities or stepsone at each end of said smaller recess portion.
 3. A tundish impact padaccording to claim 1 wherein said pad is four-sided in plan view.
 4. Atundish impact pad according to claim 3 wherein said paid has one pairof parallel sides defined by said outer surface of said sidewall.
 5. Atundish impact pad according to claim 4 wherein said longer parallelside includes said first portion of said top surface and said smallerrecess.
 6. A tundish impact pad according to claim 3 wherein said pad isrectangular in plan view.
 7. A tundish impact pad according to claim 1wherein said smaller recess portion is not coterminous with the lowertop surface portion.
 8. A tundish impact pad according to claim 7wherein said smaller recess portion does not extend as far as said endsof said lower top surface.
 9. A tundish having an inlet zone adjacent afirst end thereof and an outlet zone adjacent said opposite end thereofand an impact pad positioned on said floor of said tundish in said inletzone;said impact pad comprising a body of refractory material capable ofwithstanding contact with molten steel, said body comprising a basehaving an impact surface for molten steel, an outer sidewall extendingupwardly from said impact surface, said outer sidewall extending aroundsaid base to completely enclose it, an annular body portion connected tosaid sidewall and providing a top surface substantially parallel to saidimpact surface and defining an opening into which molten steel can bepoured, said lower surface of said annular body portion and said innerface of said sidewall defining a recess having an undercut portionextending continuously around and above said impact surface, wherein aportion of said top surface is at a lower level than said remainder ofsaid top surface and said recess beneath said portion of the top surfaceis of smaller cross-section than said remainder of said recess; andwherein said pad is positioned with said portion of said top surfacefacing said first end of said tundish.
 10. A tundish according to claim9 wherein said impact pad is of wedge-shape and said longer parallelside of said pad is positioned facing said first end of said tundish.11. A tundish according to claim 9 wherein said tundish islongitudinally-extending and of wedge shape in plan view.
 12. A tundishaccording to claim 9 wherein said tundish is rectangular in plan view.13. A tundish impact pad according to claim 2 wherein the pad isfour-sided in plan view.
 14. A tundish impact pad according to claim 13wherein that the pad has one pair of parallel sides defined by the outersurface of the sidewall.
 15. A tundish impact pad according to claim 2wherein the smaller recess portion is not coterminous with the lower topsurface portion.
 16. A tundish impact pad according to claim 15 whereinthe smaller recess portion does not extend as far as the ends of thelower top surface.
 17. A tundish impact pad according to claim 14wherein the smaller recess portion is not coterminous with the lower topsurface portion.
 18. A tundish impact pad according to claim 17 whereinthe smaller recess portion does not extend as far as the ends of thelower top surface.
 19. A tundish according to claim 10 wherein thetundish is longitudinally-extending and of wedge shape in plan view. 20.A tundish according to claim 10 wherein the tundish is rectangular inplan view.